Objective: To explore the new biomarkers for predicting the side effects of UGT1A1 genotyping directed chemotherapy. Methods: A total of 269 patients were enrolled in the present study. Each patient was determined polymorphism of UGT1A1 gene for genotyping. Serum biochemical markers including alanine aminotransferase (ALT), aspartate aminotransferase(AST), creatinine (Scr) and plasma albumin (ALB) were also analyzed routinely prior to treatment. According to the NCCN(2017V1) guidelines, the differential doses of irinotecan were set according to the genotyping of the patients. The relationships between the side effects and blood biochemical markers were analyzed by Wilcoxon's rank-sum test. Results: The overall toxic effects in patients was significantly reduced under the genotyping directed irinotecan treatment in patients. However, 31 cases (11.5%) were found with severe irinotecan specific toxic effects. Furher analysis indicated that serum AST was associated with toxic effects of irinotecan but with lower predicted value (OR=0.98, 95% confidence interval: 0.97 ~ 1.00, P<0.05; Area under the ROC curve, AUC was 0.6797). Interestingly, low ALB level before treatment was indicated significant correlation with irinotecan induced toxic effects (OR=1.51, 95% confidence interval: 1.34 ~ 1.71, P<0.05). ROC analysis showed that the area under the curve of albumin was reached up to 0.9266. However, pathological type of tumor, gender, age, and other serum biomarker were without obvious correlations with irinotecan induced toxic effects. Conclusion: Low ALB before treatment was significantly associated with irinotecan induced toxic effects in patients and it might be a potential predicting biomarker for UGT1A1 genotyping directed chemotherapy in clinic.